1. Field of the Invention
This invention relates to a cooperative type vehicle collision avoidance system and particularly relates to such systems as can be used upon aircraft for the prevention of mid-air collisions.
2. Description of the Prior Art
Recent aircraft collisions have focused national attention on the need for reliable collision avoidance equipment which is simple, safe and reliable. Presently available collision avoidance systems require a sizable amount of complex equipment which must be constantly maintained. Even with adequate maintenance, such systems are subject to failure causing a rash of whistles and buzzers to go constantly in the plane cockpits creating disturbing distractions to the aircraft pilots.
One example of such a complex system is that shown in U.S. Pat. No. 3,611,385, which incorporates the use of light generator and detector systems. As well as being complex, the response of such systems deteriorates during fog, rain and snow conditions. Also, such systems are subject to confusion by reception of signals from ground base light sources such as reflected highways, vehicle lights and radio and television antennas that are equipped with strobe lights. U.S. Pat. No. 3,708,671 shows another light generator and detector system for indicating the direction of intruder aircraft approach. This system is also subject to deterioration during rain, fog and snow conditions and again is subject to inadvertent signalling due to ground base light sources. U.S. Pat. No. 3,736,559 and U.S. Pat. No. 3,846,746 are similarly deficient in that they also rely upon light generators and detectors for signalling the presence of intruder aircraft. U.S. Pat. No. 4,104,638 shows an anti-collision radio system wherein a conventional automatic direction finder ascertains the bearing of an aicraft transmitting a modulated tone or tones. The use of multiple frequencies as suggested by this system in a collision avoidance application is impractical. Furthermore, the display interpretation time as disclosed is prohibitively long. Also, the aircraft type discrimination as disclosed is complex and is therefore subject to various faults. U.S. Pat. No. 3,310,806 shows a complex collision prevention system wherein an aircraft transmits signals indicative of its altitude and course and another aircraft receives these signals and computes the relative courses of the two aircraft. The complexity of such a system makes it impractical in terms of both cost and maintenance. U.S. Pat. No. 3,653,049 shows a collision warning system wherein a host aircraft detects the radio frequency transmissions from an intruder aircraft in its vicinity. A multi-segment antenna provides information as to the compass quadrant of the intruder aircraft and the intensity of the received signal is monitored to provide an indication of closure rates between the two aircrafts. The primary deficiency of this system is in that the intruder aircraft must be constantly transmitting a signal in order for the collision warning system to be effective.